Aromatic polyamide pulp and its production process

ABSTRACT

The aromatic polyamide pulp obtained by the process of this invention is good in dispersibility in water and good in opening property, and excellent in dispersibility of inorganic filler and wettability with and adhesion to a matrix resin such as phenol resin. Hence, an impregnated paper and molded article excellent in homogeneity and mechanical strength can be produced. Also, in the case of friction materials free from paper-making step, the filler-retention of pulp in the production process is good and such a result that the filler-dispersibility and mechanical strength of molded article are excellent is obtained, and the pulp can be utilized particularly effectively in uses as asbestos-substitutes.

This invention relates to an aromatic polyamide pulp surface-treatedwith an epoxy resin and to a process for producing the same. Moreparticularly, it relates to an aromatic polyamide pulp which is easy tohandle in the case where an aromatic polyamide pulp is dispersed andmixed with other materials as in friction materials, gasket and the likeand which gives a product excellent in mechanical properties, and to aprocess for producing the same.

Aromatic polyamides such as polyparaphenylene terephthalamide,polymetaphenylene isophthalamide and the like referred to hereinafter asaramids in some cases) are known to be useful for fiber, pulp, film andthe like which are excellent in heat resistance, mechanicalcharacteristics, electric characteristics and the like. In particular,aramid pulp obtained by fibrillating aramid fibers is useful asasbestos-substitutes. Processes for producing aramid pulp haveheretofore been proposed. As an example, Japanese Patent ApplicationKokoku No. 59-603 discloses a process for producing aramid pulp byforming a film-like material or a monofilament from an opticallyanisotropic dope of para-aromatic polyamide and then fibrillating thefilm-like material or monofilament by a mechanical shear force. Also,Japanese Patent Application Kokai No. 2-200,809 discloses a process forproducing aramid pulp directly from a solution of a polymer of ameta-aromatic polyamide, and apparatus to be used therein. When aramidfibers are to be used as reinforcing fibers, it is important that thearamid fibers are excellent in wettability with and adhesiveness to aresin or rubber which is a matrix, and from this view point, variousmethods have been proposed for the purpose of improving the wettabilityand adhesiveness between aramid fiber and matrix.

For example, Japanese Patent Application Kokai No. 62-218,425 disclosesa method of improving the adhesiveness between an aramid material and anepoxy resin in applying the epoxy resin to the surface of an aramidmaterial (short fiber, long fiber, woven fabric, sheet or the like) byimmersing in or spray-coating with an organic solvent solution of anepoxy resin and also applying a heat-treatment thereto in said case. Inaddition, Japanese Patent Application Kokai No. 62-225,539 discloses amethod of improving the adhesiveness of an aramid material to an epoxyresin by heat-treating the aramid material in the presence of an ammoniagas in the application of an epoxy resin to the surface of the aramidmaterial. However, all these methods are concerned with treatment ofaramid fibers having a fiber diameter of about 12 μm, and when thesemethods are applied to highly fibrillated aramid pulp having a fiberdiameter of 1 μm or less, the fibrils are adhered to one another tocause a problem of impairing the dispersibility and opening property ofthe aramid pulp, so that it is difficult to apply the above methods asthey are to the aramid pulp.

The object of this invention is to provide an aramid pulp which is usedas an asbestos-substitute for friction materials, gaskets and the likeand suitable for producing a product excellent in wettability with andadhesiveness to a matrix, such as phenol resin and rubber, and alsoexcellent in inorganic filler retention and exhibits high mechanicalproperties without impairing the dispersibility and opening property ofthe aramid pulp.

These and other objects are achieved by the invention, which issummarized as follows.

(1) An aromatic polyamide pulp characterized by having beensurface-treated with an epoxy resin whose glycidyl groups have beenpartially hydrolyzed and having a water content of less than 30% byweight.

(2) A process for producing an aromatic polyamide pulp surface-treatedwith an epoxy resin and having a water content of less than 30% byweight, characterized by dispersing an aromatic polyamide pulp in anaqueous epoxy 20 resin emulsion, and subjecting the same to filtering,dehydrating, drying and opening.

(3) A process for producing an aromatic polyamide pulp according to (2)above wherein an aqueous emulsion of an epoxy resin whose glycidylgroups have been partially hydrolyzed is used.

This invention is explained in detail below. The aramid used in thisinvention, that is, the total aromatic polyamide, is such that 85 mole %or more of the amide bonds are obtained from an aromatic ring diamineand aromatic ring dicarboxylic acid components.

Specific examples thereof include polyparaphenylene terephthalamide,polymetaphenylene terephthalamide, polyparabenzamide,poly-4,4'-diaminobenzanilide, polyparaphenylene-2,6-naphthalic amide,copolyparaphenylene/4,4' (3,3'-dimethylbiphenylene) terephthalamide,copolyparaphenylene/2,5-pyridylene terephthalamide, polyorthophenylenephthalamide, polymetaphenylene phthalamide, poly paraphenylenephthalamide, polyorthophenylene isophthalamide, polymetaphenyleneisophthalamide, polyparaphenylene isophthalamide, polyorthophenyleneterephthalamide, poly-1,5-naphthalene phthalamide, poly-4,4'-diphenyleneorthophthalamide, poly-4,4'-diphenylene isophthalamide,poly-1,4-naphthalene phthalamide, poly-1,4-naphthalene isophthalamide,poly-1,5-naphthalene isophthalamide and the like; aromatic polyamidescontaining alicyclic amine, representatives of which are theabove-mentioned aromatic diamines whose benzene nucleus has beenpartially replaced with piperazine, 1,5-dimethylpiperazine or2,5-diethylenepiperazine; copolymers of aromatic polyamide containingtwo phenyl groups in which the aromatic diamines are bonded through anether linkage such as 3,3' oxydiphenylenediamine,3,4'-oxydiphenylenediamine or the like, or a group such as --S--,--S02--, --CO--, --NH-- or the like, for example,poly-3,3'-oxydiphenylene terephthalamide/polyparaphenyleneterephthalamide copolymer, poly-3,4-oxydiphenyleneterephthalamide/polyparaphenylene terephthalamide copolymer; and thelike.

The term "aramid pulp" used herein means one having the form that aramidfibers are highly fibrillated, whose specific surface area as measuredby the BET method is preferably 3 to 25 m² /g, and whose freeness asmeasured by the Canadian standard method in the "Pulp Freeness TestMethod" of JIS P 8121 is preferably 40 to 700 ml, more preferably 100 to700 ml, and most preferably 150-700 ml.

The process for producing the aramid pulp is not particularly limitedand such processes as mentioned in, for example, Japanese PatentApplication Kokoku No. 59 603, Japanese Patent Application Kokoku No.2-200,809 and the like can be applied.

The epoxy resin for preparing the aqueous epoxy resin emulsion used inthis invention is not limited as far as it can achieve the purpose ofthis invention. For example, the following can be used:

Bisphenol A type liquid epoxy resins such as Sumiepoxy ELA-128 (tradename of Sumitomo Chemical Co., Ltd.) and the like; bisphenol A typesolid epoxy resins such as Sumiepoxy ELA-012 (trade name of SumitomoChemical Co., Ltd.) and the like; orthocresol novolak type epoxy resinssuch as Sumiepoxy ESCN-220L (trade name of Sumitomo Chemical Co., Ltd.)and the like; triglycidylamine type epoxy resins such as SumiepoxyELM-120 (trade name of Sumitomo Chemical Co., Ltd.) and the like;tetraglycidylamine type epoxy resins such as Sumiepoxy ELM-434 (tradename of Sumitomo Chemical Co., Ltd.) and the like; etc.

Among them, the tetrafunctional tetraglycidylamine type epoxy resin ispreferred in respect of enhancing adhesiveness. Furthermore, the epoxyequivalents of these epoxy resins are preferably 1,000 g/eq. or less.When the epoxy equivalent exceeds 1,000 g/eq., a sufficient adhesivenessto a matrix cannot be obtained.

As the method of producing an aqueous emulsion using the above epoxyresin, there can be applied a generally used method as it is. That is,an aqueous epoxy resin emulsion is obtained, for example, by dispersingan epoxy resin in water by a high speed stirring in the presence of anonionic surface active agent such as an ether compound ofpolyoxyethylene and a higher fatty acid alcohol or the like.

In this case, the epoxy resin/surface active agent composition ratio byweight may be varied depending upon the kind of epoxy resin and the kindof surface active agent; however, in view of the stability andadhesiveness of emulsion, the composition ratio is preferably selectedin the range of 97/3 to 70/30. It is also possible to use commerciallyavailable epoxy resin emulsions such as ANS-1001 and ANS-1006 (tradenames of Takemoto Yushi K. K.) and the like which are emulsions of anepoxy resin. In view of uniformity of treatment, the particle size ofemulsion is preferably 15 μm or less in diameter, more preferably 5 μmor less in diameter. In order to increase the amount of the epoxy resinadsorbed on the pulp in the treating solution, it is particularlypreferable to use an emulsion of an epoxy resin whose glycidyl groupshave been partially hydrolyzed into glycol groups because in this casethe epoxy resin is 100% adsorbed on the aramid pulp without using noother particular means. As a method for preparing the emulsion of anepoxy resin whose glycidyl groups have been partially hydrolyzed intoglycol groups, there can be used a method of preparing an emulsiondispersion using as the starting material an epoxy resin hydrolyzed by agenerally known method. It is also possible to use a method comprisingpreparing an epoxy resin emulsion by a conventional method as describedbelow and then hydrolyzing the resulting emulsion. According to thelatter method, a uniform, stable emulsion can be obtained easily. Inorder to hydrolyze the emulsion, various methods can be used de pendingupon the kind of the emulsion and it is the simplest and preferable tosubject the emulsion as such to heat-treatment. As a result ofhydrolysis, a part of the epoxy groups of the epoxy resin is split to aglycol group. The reaction percentage of the hydrolysis is preferably10% or more, more preferably at least 20% but less than 90%, of theinitially existing epoxy groups.

When the hydrolysis is insufficient, the adsorption of the resin on thepulp tends to become insufficient, and when the hydrolysis is excessive,the performance of the treated pulp such as adhesiveness of the pulp tophenol resin or the like is reduced. In the hydrolysis, an increase ofthe molecular weight of the epoxy resin due to condensation reaction iscaused simultaneously with the formation of glycol groups; however, asfar as it does not adversely affect the stability of the emulsion it hasno particular problem in this invention. The reaction percentage ofhydrolysis can be calculated from the following equation by measuringthe epoxy equivalents:

Conversion (%)=100×{1-(WPEi/WPEx)} wherein WPEi is the initial epoxyequivalent and WPEx is the epoxy equivalent after the hydrolysis.

The suitable hydrolysis conditions are varied depending upon the kind ofthe epoxy resin used, the kind of surface active agent used, thecompositions and con centrations thereof and the like and are not alwayslimited. As an example thereof, in the case of a nonionic emulsion ofSumiepoxy ELM-434 (trade name of Sumitomo Chemical Co., Ltd.) andANS-1006 (manufactured by Take moto Yushi K. K.), which aretetraglycidylamine type epoxy resins, the hydrolysis can be effected inthe following manner: The emulsion can be heat-treated at a temperatureof 650C for 130 hours to obtain an emulsion of an epoxy resin whoseobjective glycidyl groups have been partially hydrolyzed into glycolgroups. By this treatment, the epoxy equivalent is increased from about120 g/eq. to about 240 g/eq. In this case, the reaction percentage isabout 50%. Also, the same effect can be obtained by allowing the epoxyresin emulsion to stand at room temperature for 3 to 6 months. Moreover,a catalyst such as an acid, an alkali, an amine or the like can be usedto promote the hydrolysis reaction.

The treatment of aramid pulp with the above-mentioned epoxy resinemulsion, the glycidyl groups of which have been partially hydrolyzed,is effected, for example, by the following method: First of all, thearamid pulp is dispersed in water to the extent that a sufficientfluidity is obtained. The concentration of the aramid pulp dispersed inthe dispersion is varied depending upon the specific surface area andfreeness of the pulp used, and is preferably selected in the range of0.5 to 5% by weight. In order to uniformly disperse the pulp, aconventional propeller type stirrer can be used. A beater for pulp whichis used for dispersing usual linter pulp is particularly effective forachieving the uniform dispersion.

Subsequently, while the dispersion is stirred, the desired amount of theabove-mentioned epoxy emulsion, the glycidyl groups of which have beenpartially hydrolyzed, is dropwise added. The amount of the emulsionadded is such that the amount of the epoxy resin adhered is preferably0.3 to 20% by weight, more preferably 0.5 to 10% by weight and mostpreferably 1 to 6% by weight, based on the absolute dry weight of pulp.When the amount of the epoxy resin adhered is 0.3% by weight or less,the desired mechanical properties are not achieved and a sufficientepoxy resin treating effect is not obtained. When it is 20% by weight ormore, it shows a tendency that the dispersibility of the pulp becomesbad, and an effect corresponding to the amount of the resin adhered isnot obtained, so that it is inferior in economy.

After completion of the dropwise addition of the emulsion, the stirringof the emulsion is continued as it is for 5 to 60 minutes to adsorb theepoxy resin on the pulp surface. According to the process of thisinvention, the epoxy resin is substantially 100% adsorbed on the aramidpulp surface only by the above treatment. By treating the aramid pulpwith the epoxy resin emulsion, it is possible to produce an aromaticpolyamide pulp excellent in adhesiveness to phenol resin or the like.

After the adsorption of the emulsion, the dispersion is filtered in aconventional manner. The thus filtered surfacetreated aramid pulp issubjected to a dehydrator such as a centrifugal separator or the like toreduce the water content and then dried so that the water contentbecomes less than 30% by weight, preferably 3% by weight or more but 10%by weight or less. When the water content is too low, the electrostaticproperty is deteriorated and handling becomes difficult, and when it istoo high, the opening property and compatibility with a filler tend tobe deteriorated.

The drying temperature may be varied depending upon the kind of theepoxy resin used for the surface treatment; however, in general, it ispreferably conducted at a temperature of 100° C. or lower, morepreferably 50° C. or lower. When the drying temperature is too high, thecuring and fusion of the epoxy resin is caused, so that the subsequentopening treatment becomes insufficient. Hence, even when used infriction materials, gaskets and the like, the dispersion of pulp becomesununiform and in addition the expected adhesion effect is not obtainedin some cases. In order to shorten the drying time, the surfacetreatedaramid pulp which has been dehydrated can be formed into small blocksand then dried in a conventional oven. Also, according to a method usingan apparatus in which much wind is sent such as a fluidized bed, it ispossible to conduct drying around room temperature in a relatively shortperiod of time.

The surface-treated aramid pulp which has been dried is subsequentlysubjected to opening. In the convention al surface-treatment which hasheretofore been conducted, fibrils of pulp are adhered to one anotherduring the drying, and hence, sufficient opening is impossible; however, since in the surface-treated aramid pulp according to thisinvention, the particles of the epoxy resin attached to the surface ofthe pulp are fine, even when the pulp is subjected to opening in thefollowing manner, a pulp having the same dispersibility andfiller-retention as untreated pulp is obtained.

The opening can be conducted by use of a grinding apparatus such ashammer mill, ACM pulverizer, corn mill, roll crusher, screw intermediatepulverizer, ring-roller mill, stamp mill, rod mill, impact crusher, jetmill, edge runner, tower type mill, colloid mill or the like; a fixedtype mixer in which mixing is conducted by rotating a screw, a ribbon, afinger prong, a Z-shaped blade or the like in a cylindrical orgutter-like vessel; or the like.

Preferably, preliminary opening is conducted by the fixed type mixer andthereafter the main opening is conducted by means of a pulverizer suchas jet mil or the like, whereby favorably opened aramid pulp which hasbeen surface-treated with an epoxy resin is obtained; however, theprocess of this invention is not limited thereto.

The surface-treated aramid pulp of this invention has a high absorptionbetween epoxy resin and aramid pulp, and hence, the epoxy resin is notstripped from the surface of the aramid pulp even when subjected to theabove opening treatment, and the performance of the pulp is not affectedat all by the opening treatment.

The opened, surface-treated aramid pulp can be compressed by anappropriate method to facilitate the handling in conveyance, weighingand the like. Even when the surface-treated aramid pulp of thisinvention is compressed to a bulk density of 0.05 to 0.1 g/cc, thedispersibility and the like in practical use are not affected thereby.

EXAMPLES

This invention is explained in more detail below referring to Examples,and in the Examples, the evaluation of aramid pulp was conducted by themethods described below.

Method of evaluating aramid pulp

1. Evaluation method 1

Evaluation of length at break of aramid pulp/inorganic filler compositepaper

(1) Papermaking

Aramid pulp in an amount corresponding to 6.25 g of pulp in terms ofabsolute dry weight and 4.2 g to 8.0 g of diatomaceous earth (the weightwas adjusted so that the weight ratio of the pulp/diatomaceous earthafter papermaking became 60/40 depending on the filler-retention of thepulp used) were weighed and dispersed in one liter of water at 3,000 rpmfor 3 minutes in a 2-liter capacity standard pulp beater (manufacturedby Kumagai Riki Kogyo K. K.). Subsequently, papermaking was conducted ina conventional manner using a 25-cm square shaped sheet machine(manufactured by Kumagai Riki Kogyo K. K.) and a # 80-mesh wire net, andthereafter dried at 120° C. for two hours to obtain a 25-cm squarearamid paper/diatomaceous earth composite paper (weight ratio of aramidpulp/diatomaceous earth: about 60/40) having a 5 unit weight of about167 g/m2.

(2) Tensile test

The necessary sheets of test piece having a size of 15×200 mm were cutfrom the above aramid pulp/diatomaceous earth composite paper and thebasis weight was determined. Subsequently, a tensile test was conductedunder the following conditions to determine the length at break by thefollowing equation:

Test piece size: 15 mm×200 mm

Gauge length: 100 mm

Crosshead speed: 10 mm/min

    Breaking Length (km)  tensile load (kgf)!/ test plece wldth (mm)×test specimen basis weight (g/m2)!×1000

2. Evaluation method 2

Evaluation using aramid pulp/inorganic filler/phenol resin clutch facingmodel molded article

(1) Paper-making

Aramid pulp of a weight corresponding to 6.25 g of pulp in terms ofabsolute dry weight and 4.2 g to 8.0 g of diatomaceous earth (the weightwas adjusted so that the pulp/diatomaceous earth weight ratio afterpaper making became 60/40 depending on the filler-retention of the pulpused) were weighed, and then dispersed in one liter of water at 3,000rpm for three minutes in a 2 liter capacity standard pulp beater(manufactured by Kumagai Riki Kogyo K. K.). Subsequently, the dispersionwas subjected to papermaking in a conventional manner in a square shapedsheet machine of 25-cm square (manufactured by Kumagai Riki Kogyo K.

K.) using a # 80-mesh wire net, and thereafter dried at 120° C. for twohours to obtain a 25-cm square aramid pulp/diatomaceous earth compositepaper (aramid/diatomaceous earth weight ratio: about 60/40) having aunit weight of about 167 g/m².

(2) Impregnation with phenol resin

Several sheets of a sample of a size of 50 mm×100 mm were cut from theabove aramid paper and weighed. Subsequently, a 45% methanol solution ofa modified resol type phenol resin PR-SCI-3 (trade name of SumitomoDurez Co., Ltd.)! was prepared by dilution. The above composite papersample sheets were uniformly impregnated with this resin solution sothat the aramid pulp/diatomaceous earth/resin weight ratio became60/40/35, and then dried at 50° C. for 30 minutes to prepare animpregnated prepreg.

(3) Press-molding

Two sheets of the above prepreg were put one on the other, a spacer of0.6 mm in thickness was placed and the resulting assembly waspress-molded at 180° C. and at 100 Kgf/cm² for five minutes, andthereafter treated in an oven at 180° C. for two hours to post-cure theresin, there by obtaining a clutch facing model molded article having aporosity of 50%.

(4) Tensile test

The tensile strength of the molded article obtained by the above methodwas measured under the following conditions:

Test piece size: 10 mm×100 mm

Gauge length: 50 mm

Crosshead speed: 5 mm/min

3. Evaluation method 3 (measurement of freeness)

The freeness of aramid pulp was measured according to the Canadianstandard method in the "Pulp Freeness Test Method" of JIS P 8121.

4. Evaluation method 4 (Measurement of amount of epoxy resin adhered)

The amount of the epoxy resin adhered to the aramid pulp was determinedby the following equation form the COD of the filtrate after thesurface-treatment and COD of the epoxy emulsion used in thesurface-treatment: Amount of epoxy resin adhered(%)=Ew/(Pw+Ew)×(1-Ta/Tb)×100, wherein

Ew: Weight of epoxy resin solids in epoxy resin emulsion (g)

Pw: Weight of pulp used in surface-treatment (g)

Ta: COD of filtrate after surface-treatment (mg/l)

Tb: COD of epoxy resin emulsion used in surface-treatment (mg/l)

5. Evaluation method 5 (evaluation of friction material in the form ofmodel molded article)

By the following method, a model molded article of a friction materialwas prepared and the performance there 5 of was evaluated:

(1) Composition (% by weight)

    ______________________________________                                        Aramid pulp                   5.0                                             Rock wool RF-5164 (manufactured by Tsuchiya Kaolin K. K.)                                                   5.0                                             Barium sulfate                47.5                                            Kaolin                        32.5                                            Phenol resin PR-50252 (Sumitomo Durez)                                                                      10.0                                            ______________________________________                                    

(2) Mixing

In a Lodige Ploughshare mixer M-20 Model (Matsuzaka Boeki K.K.) wereplaced 100 g of pulp, 100 g of rock wool, 950 g of barium sulfate, 650 gof kaolin and 200 g of phenol resin (2 kg in total), and they were mixedat 230 rpm (main shaft) at 6,000 rpm (chopper) for five minutes toobtain a mixture.

(3) Measurement of filler-retention of mixture

In order to evaluate the stability of the mixture, the filler-retentionof the mixture was measured by the following method:

1) A 60-mesh (0.25 mm) screen having a diameter of 100 mm was set in aSHAKER VXR type shaker (manufactured by JANKE & KUNKEL GMBH & CO.).

2) 20 g of the mixture sample was weighed (W1), and put on the screen.

3) The screen was shaken at 1,600 rpm for ten minutes.

4) Powder which fell on a receiver was weighed (W2).

5) Subsequently, the filler-retention was calculated. Filler-retention={(W1-W2)/W1}×100

(4) Measurement of load at break of preform

For evaluating the handleability of preform, a preform was prepared bythe following method and the load at which it was broken was measured:

1) In a mold of 100 mm in width, 150 mm in length and 50 mm in depth wasplaced 200 g of the mixture.

2) The mixture was pressed at room temperature at 270 kgf/cm2 for 15minutes to obtain a preform of 7 mm in thickness.

3) The preform thus obtained was subjected to flex test under thefollowing conditions to determine the load at break:

Span: 120 mm

Crosshead speed: 10 mm/min

Test piece size: 100 mm×150 mm×7 mm

(5) Evaluation of dispersibility

For evaluating the dispersibility of pulp, a molded article was preparedand evaluated by the following method:

1) In a mold of 15 mm in width, 150 mm in length and 50 mm in depth wasplaced 33 g of the mixture.

2) The mixture was heat-pressed at 1300C at 45 kgf/cm2 for 15 minutes toobtain a molded article having a thickness of 12 mm.

3) The molded article was post-cured in an oven at 180° C. for one hourto complete the curing of the phenol resin.

4) The molded article thus obtained was mechanically divided into twoparts with a chisel or the like and the broken face obtained wasobserved to count the number of pills of aramid pulp having a size ofnot less than 1 mm in diameter, thereby evaluating the dispersibility ofpulp.

6. Evaluation method 6 (Measurement of water content)

The water content referred to herein can be determined by the followingcalculation equation:

    Water content (wt. %)={(W1 -W2)/W1 }×100

wherein

W1: Weight of pulp in the hydrous form.

W2: Weight of pulp after absolute drying.

EXAMPLE 1

In 100 liters of deionized water was dispersed 1.007 kg of Twaron 1099trade name of Nippon Aramid Yugen Kaisha for pulp of poly(paraphenyleneterephthalamide) having a specific surface area by the BET method of 16m2/g and a water content of 6% by weight! in a 200-liter reactor. Tothis aramid pulp dispersion was dropwise added with stirring 313 g of atetraglycidyl amine type epoxy resin emulsion dispersion whose epoxyequivalent was adjusted to 270 g/eq. by heat-treatment at 65° C. for 130hours ANS 1006 20 (trade name of Takemoto Yushi K. K.)!, and thereafter,the stirring was continued at room temperature for 30 minutes.Subsequently, the dispersion was filtered and the pulp separated byfiltration was dehydrated so that the water content became about 50% byweight to obtain a water-containing aramid pulp which had beensurfacetreated with an epoxy resin whose glycidyl groups had beenpartially hydrolyzed.

This water-containing aramid pulp was dried at 50° C. until the waterbecame 6% by weight, and thereafter, subjected to preliminary opening bymeans of Universal Mixer EM25B Model (manufactured by TSUKISHIMA KIKAICO., LTD.) and then to main opening by means of a single track jet millSTJ-200 Model (manufactured by Seishin Kigyo K. K.) to obtain an openedaramid pulp surfacetreated with an epoxy resin which pulp had a watercontent of 5% by weight. The aramid pulp thus obtained was evaluated bythe above-mentioned methods (1) to (5) to obtain the results shown inTable 1.

EXAMPLE 2

The same treatment as in Example 1 was applied to Twaron 1095 (tradename of Nippon Aramid Yugen Kaisha for pulp of polyparaphenyleneterephthalamide having a specific surface area by the BET method of 6m2/g and a water content of 6% by weight), and the evaluation wasconducted by the above methods to obtain the results 21 shown in Table1.

Comparative Example 1

Twaron D1099 (the same as above) which had not been subjected to thesurface-treatment with the epoxy resin was evaluated by the abovemethods to obtain the results shown in Table 1.

Comparative Example 2

Twaron 1095 (the same as above) which had not been subjected tosurface-treatment with the epoxy resin was evaluated by the abovemethods to obtain the results shown in Table 1.

Comparative Example 3

The same procedure as in Example 1 was repeated, except that atetraglycidyl type epoxy resin emulsion dispersion which had not beensubjected to heat-treatment and hence not hydrolyzed ANS-1006 (tradename of Takemoto Yushi K. K., epoxy equivalent: 130 g/eq.) was used asit was, to obtain an aramid pulp surface-treated with the epoxy resin.This aramid pulp was evaluated by the above methods to obtain theresults shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                         Comp.   Comp.         Comp.                                             Ex. 1 Ex. 1   Ex. 3   Ex. 2 Ex. 2                                  ______________________________________                                        Breaking length of                                                                          0.22    0.17   --     0.15  0.04                                composite paper (km)                                                          Tensile strength of                                                                        4.0     3.3     3.6   3.5   3.3                                  resin-impregnated model                                                       molded article (kgf/mm2)                                                      Freeness (ml)                                                                              350     350      90   600   580                                  Amount of epoxy resin                                                                      5       0        3    5     0                                    adhered (%)                                                                   COD of filtrate (mg/l)                                                                     6       --      460   7     --                                   COD of epoxy emulsion                                                                      950     --      950   950   --                                   (ml/l)                                                                        Characteristics of                                                            friction material model                                                       molded article                                                                Filler-retention (%)                                                                       8       8        76   50    50                                   Load at break of perform                                                                   2.7     2.4     2.5   2.2   2.2                                  (kgf)                                                                         Dispersibility (number of                                                                  0       0        4    0     0                                    pills)                                                                        ______________________________________                                    

We claim:
 1. An aromatic polyamide pulp, characterized by having beensurface treated with an epoxy resin whose glycidyl groups have beenpartially hydrolyzed from at least 10% to less than 90% of the initiallyexisting epoxy groups to increase the amount of the epoxy resin adsorbedon the pulp so that the amount of epoxy resin that is adhered to thepulp is from 0.3% to 20%, by weight, based on the absolute dry weight ofpulp, and having a water content of less than 30% by weight.
 2. Aprocess for producing an aromatic polyamide pulp surface treated with anepoxy resin whose glycidyl groups have been partially hydrolyzed from atleast 10% to less than 90% of the initially existing epoxy groups toincrease the amount of the epoxy resin adsorbed on the pulp so that theamount of epoxy resin that is adhered to the pulp is from 0.3% to 20%,by weight, based on the absolute dry weight of pulp, and having a watercontent of less than 30% by weight, characterized by dispersing anaromatic polyamide in an aqueous epoxy resin emulsion, and thensubjecting the dispersion to filtration, dehydration, drying andopening.